Electric pulse-forming shot-firing device



1952 G. MUFFLY 2,623,922

ELECTRIC PULSE-FORMING SHOT-FIRING osvxcs Filed April 17, 1950D5ETNPSTOR AVA'AVAVA 12 1 l TO HOT MOVE-NT MMUNICJRTION CIRCUIT -27NIJ-L1$32QOND INVENTOR. BR M FFLY 1 ms ATTORNEY Patented Dec. 30, 1952ELECTRIC PULSE-FORIVHNG SHOT-FIRING- DEVICE Gary Mufliy, Penn Township,Allegheny County, Pa., assignor to Gulf Research & Development Company,Pittsburgh, Pa., a corporation of Delaware Application April 17, 1550,Serial No. 156,303

11 Claims. (Cl. 175 -115) This invention concerns an apparatus forfiring electric detonators and is particularly useful inseismograph-prospecting operations in that the apparatus facilitates theaccurate, unambiguous and definite recording of the instant at which theexplosive detonates.

In seismograph geophysical-prospecting operations itis customary to fireone or more explosive charges usually but not necessarily buried in theearth, and to record distant earth tremors resulting from the explosion.A study is made of the travel times of the tremors and from an analysisof such travel times geophysicists may in known manner deduce thestructure of the underlying rock formations. In order to measure thetravel time of the various tremors or seismic disturbances produced bythe dynamite explosion, it is necessary to record along with theseismograph tremors the instant at which the shock or tremor isinitiated, namely, the instant at which the tremor-producing explosionoccurred. The instant is ordinarily termed the shot moment.

One way in which the shot moment has heretofore been obtained is to drawa so-called shotmoment wire around the dynamite so that upon explosionof the dynamite the shot-moment circuit is ruptured producing adeflection (called the shot-moment kick) on one of the galvanometerswhich record on the same recording medium as the galvanometers whichrecord the tremors received by the seismographs. There are numerousdifliculties associated with this manner of obtaining the shot moment.It requires the use of additional wires running down the shot hole, twowires being required for the electric detonator and two separate wiresfor the shot-moment circuit. Furthermore, the shot-moment wires may beviolently blown out of the shot hole immediately after the explosion,with the result that the insulation is at least partially destroyed fromthe shot-moment wires whereupon the wires may ground or short-circuit,thus producing spurious kicks on the shot-moment record, which signalsare often mistaken for the true shot-moment particularly if the latteris weak or interfered with as by static or other disturbances. Inaddition,- there is always some danger that current from the shot-momentcircuit may leak into the detonator circuit and prematurely fire theshot.

In view of the above-mentioned difficulties an attempt has been made toobtain the shot moment from the detonator circuit itself. At first thisled to some inaccuracies in the shot moment, because the older types ofelectric detonators had varying amounts of time delay between the fusingof the detonator bridge wire and the actual detonation of the explosive.These delays often amounted to several milli-seconds and constituted asource of error in the subsequent interpretation of the seismogram.However, the manufacturers of electric detonators soon developed animproved type of detonator for use in .seismograph operations. The newdetonators have little or no thermal delay less than one milli-second)and this type of no-delay detonator is now customarily employed in allseismographprospecting operations.

However, in spite of the use of detonators having substantially nodelay, many of the difliculties inherent in obtaining the shot momentfrom the detonator circuit still remain due to the fact that thedetonator wires can and often do shortcircuit after the explosionresulting in confused and erratic shot-moment kicks on the record. In

. fact, the explosion gases themselves may contain sufilcient ionizedmaterial to carry the detonator current for an appreciable intervalafter the detonator bridge wire has severed. Furthermore, theassociation of signalling devices with the detonator circuit introducesa hazard. By the use of my invention an unmistakable, unambiguous shotmomentmay be obtained from the detonator circuit. Furthermore, the shotmoment obtained by the use of my invention is of controlled and uniformcharacter so that the interpreter of the seismogram may easily recognizethe shot-moment kick and accurately ascertain the true shot moment. Atthe same time the hazard incident to the association of signallingcircuits is minimized.

It is accordingly an object of my invention to provide adetonator-firing apparatus which produces an easily recognizableshot-moment pulse.

It is another object of my invention to provide a detonator-firingapparatus having a high degree of safety against the danger ofelectrical energy being transferred from the signalling or recordingcircuit to the detonator circuit.

Another object of my invention is to provide a detonator-firingapparatus Which eliminates time delay between actual explosion and therecorded shot-moment kick.

Another object of my invention is to provide a detonator-firingapparatus which eliminates false shot-moment indications due to noisycircuits or poor connections or short-circuits in the detonator circuit.

Another object of my invention is to provide a detonator-firingapparatus which is capable 3 or firing several electric detonatorssubstantially simultaneously.

Another object of my invention is to provide a safeelectric-detonator-firing apparatus which may be used either fortripping radio-signalling circuits or for direct connection inoscillograph or telephone circuits.

It is a further object of my invention to provide a detonator-firingapparatus which produces accurate shot-moment indications having asharp, uniform and unambiguous character.

It is another object of this invention to provide a detonator-firingapparatus characterized by simplicity and a high degree of reliabilityand safety.

These and other objects of my invention are accomplished by theapparatus described in this specification of which the drawing forms apart, and in which Figure 1 is a schematic wiring diagram apparatus ofmy invention;

Figure 2 shows an oscillogram of the current applied by my apparatus toan electric detonator; and

Figure 3 shows an oscillogram of a typical shotmoment impulse obtainedby the use of the apparatus of my invention.

of the The apparatus of my invention comprises a hand-driven source ofelectrical energy which charges a condenser and thereafter closes aswitch between the condenser and the detonator circuit when thegenerator has attained operating speed and the condenser is charged. Thecondenser-detonator circuit is provided with a seriesparallel network ofresistors arranged sothat the charge can under no circumstances remainon the condenser more than a few milli-seconds, and so that theshot-moment pulse which is transmitted to the shot-moment-recordingcircuit is of a definite, predetermined, uniform character which issubstantially independent of the characteristics either purposely oraccidentally imparted to the detonator circuit. Thus the detonator,which is of the low-thermal-delay type now customarily used inseismograph shooting, will either fire during the milli-second in whichcurrent is applied to it or, under exceptional circumstances, will notfire at all and may be detonated subsequently when such exceptionalcircumstances have been corrected. Furthermore, the shape of theshot-moment kick is predetermined and is therefore easily recognizableby the interpreter of the seismogram.

Referring to Figure 1, numerial I indicates a direct-current electricgenerator such as is customarily used in manually-operated blastingmachines and which is operated by energetically pushing handle 2 or somesimilar manuallyoperated means driving means 2 is arranged so thatsubstantially at the end of the stroke it mechanically closes a switch 3whose function in the circuit will become evident later. The switch 3 isarranged so that it is normally open, but closure thereof takes placeafter the generator has reached operating speed, that is, the generatoris delivering electrical energy at the time switch 3 is closed.

Connected in series with the generator I is a resistor 4 and a condenser5. The resistor 4 has a resistance sufficiently high so that should anelectric detonator be connected to the detonator terminals without thecondenser, firing of the for driving the generator I. The

in case the condenser should fail. The resistor 4 however issufiiciently low in resistance so that the generator I may chargecondenser 5 to a high voltage in a relatively short time, that is, inthe time normally taken to manually actuate the driving means 2. Thus,the generator I transfers its electrical energy to the condenser 5during the operating stroke of the driving means 2. It has been foundthat with the customary pushdown type of blasting generator, theresistor 4 may be of the order of 600 ohms. In order to prevent asustained charge from remaining on the condenser 5, the latter isshunted by a resistor 8 which may be of the order of 50,000 ohms. Thisvalue of resistor 6 is suificiently high to present substantially noload on the generator I and yet be capable of discharging the condenser5 in a few seconds if normal firing does not otherwise do so. Condenser5 is of a sufficiently large capacity to' store substantially moreenergy at the voltage generated by generator I than is required to firethe type of electric-detonator employed in seismograph operations. Ithas been found that a capacity of 20 to 100 mfd. is satisfactory. Thecondenser 5 may be of the electrolytic type and may of course be in oneor more sections as is customary in high-capacity condensers.

Connected to the terminals of condenser 5 is a series circuit comprisingthe switch 3 mentioned above, the primary winding I3 of a transformer I(which is to be described in more detail later) and a resistor 8. Thedetonator itself is indicated in Figure 1 by the resistance 9 and isconnected across the terminals Ma and Nb of resistor 8 so that thedetonator 9 is in parallel with resistor 8. The purpose of resistor 8 isto assure that the energy in the condenser 5 will be practically alldissipated within one milli-second even though the detonator circuitshould accidentally be of too high a resistance to discharge thecondenser rapidly, due to a poor connection or the like. Without theresistor 8, a poor detonator circuit might cause firing severalmilli-seconds after the shot-moment kick, but by employing the resistor8 the detonator w ll either fire before the condenser is substantiallydischarged or not fire at all. Thus resistor 8 is a desirable element toassure that delayed firing will never occur. It has been found that aresistance of 20 ohms is a satisfactory valueto use for resistor 8 ifused with a condenser 5 at about 50 mfd. The function of transformer I,which will be described in more detail later, is to transfer the pulseto a radio, telephone or other communication circuit which reaches tothe recording station so that the shot-moment pulse may be recorded onthe seismogram with the records of the seismographs customarilyemployed. a

The operation of the apparatus is therefore as follows: Mechanicalenergy imparted through the handle 2 to the generator I is convertedinto electrical energy by the generator and transferred to condenser 5.At the end of the stroke of handle 2, switch 3 is closed, whereupon theenergy stored in the condenser discharges through the transformerwinding I3 and resistor 8 building up across this resistor suflicientvoltage to fire the detonator connected thereto.

Figure 2 shows a typical oscillogram of the type of voltage or currentpulse which is delivered by the apparatus of Figure 1 to the resistor 8detonator would in no event take place. The

with a detonator connected as shown. Up to the instant 10 no currentflows in the detonator. At the instant 10 switch 3 closes and a currentstarts to flow through resistor 8 delivering across its terminals apotential which has been observed to be of the order of 75 volts.Thereafter, the potential decays exponentially in the well-known mannercharacteristic of a condenser discharging through a resistance. Itsduration will depend on the resistance of the detonator circuit inparallel combination with resistor 8 and should fall between about .001sec. for a high resistance circuit and about .00005. sec. for alow'resistanoe circuit. The transformer I is of a type which introducessubstantially no inductance into the circuit.

Transformer 1 which transfers the pulse of Figure 2 to the communicationcircuit is of a saturable-core type. Satisfactory results have beenobtained when the primary winding l3 of transformer 1 consisted of 23turns of ordinary copper magnet wire. The transformer I may have apartly laminated core ll having a relatively small cross-section so thata pulse of only a moderate amplitude may be transmitted. A core whichhas been found to be satisfactory has solid legs of %-inch diameter S.A. E. 1020 steel inserted in each coil, and a connecting leg of about byA" minimum cross-section made up of laminations of a high-permeabilityalloy, as for example mu-metal." The solid legs tend to suppress highfrequencies which might accidentally get into the timing circuit andkeep them from passing through the transformer to the detonator circuit.The mu-metal laminations provide easy saturation to control the pulseamplitude, and also limit the transfer of stray energy.

I Preferably the secondary should be wound with resistance wire andwound with substantially more turns than the primary I3. It hasbeenfound that a resistance-wire secondary winding of approximately 2400ohms and comprising 750 turns is satisfactory. The transformer 1 is of aclosed-core type and has its primary and secondary windings on separatelegs of the core.

The transformer 8 will produce a large voltage pulse in an open circuitfor tripping electrontube trigger circuits in radio-relay apparatus ifshot moment is to be conveyed by radio, and the transformer will producea pulse of limited current into a low-resistance circuit such asan'oscillograph or a telephone line leading directly to an oscillograph.The transformer I by virtue of its high secondary resistance, its easilysaturable small-cross-section core, and the physical separation of theprimary and secondary windings on separate legs of'the core, also actsas a safety device which prevents any possibility of stray current fromthe shot-moment communication circuit from getting into the detonatorcircuit. The use of resistance in the secondary winding itself ratherthan incorporating it in a separate resistor is merely a safety measureto avoid the possibility that the resistor might be short-circuited andallow stray current in the timing circuit to go through the transformerto the detonator circuit.

Figure 3showsa typical oscillogram of the typeof voltage pulse which isdelivered by the apparatus of Figure 1 to a shot-moment communicationcircuit connected to the terminals of the secondary winding I2. Thispulse has a sharp kick IS in one direction followed by a very fiatdeflection in the the appearance of a unidirectional kick whose totalduration is of the order of one-tenth millisecond as indicated in Figure3. Experiments with various commercial brands of low-thermal-delayelectric detonators obtained from various manufacturers have shown thatunder normal conditions thedetonators all fire within 1 milli-second ofthe time indicated by the peak I5 of the recorded pulse of Figure 3.This is well within the required time accuracy forseismograph-prospecting purposes. that even under marginal conditions,the maximum delay is 2 milli-seconds. Experiments have also shown thatseveral detonators may be connected in series across the terminals Ilaand Nb of Figure 1, and under normal conditions all will fire within 1milli-second of each other and of the peak l5 of the recorded pulse ofFigure 3. The pulse form shown in Figure 3 is that observed with ahigh-speed oscillograph, such as a cathode-ray tube. With such aninstrument, the height and duration of the observed pulse will vary withthe detonator-circuit resistance. However, this pulse is ordinarilyrecorded in seismograph field operations by means of a galvanometerelement having a natural'frequency of perhaps or 200 cycles per second.The pulse of Figure 3 lasts for such a. short time compared to theperiod of the usual galvanometer that it is in-efiect a ballistic kickwhich is proportional to the flux change occuring in the transformer asit is magnetized to satura-- tion by the firing current. 7

Experiments indicate that the ballistic kick is nearly equivalent forany value of detonator-circuit resistance since the amplitude variationsare offset by variations in duration of the pulse. The actual recordmade by the usual time of seismograph galvanometer is consequently notonly uniform, but it is characteristic of the natural frequency and thedamping constant of the galvanometer. As long as the same galvanometerisused, or one of the same characteristics, the shot' used incommunication circuits. At a higher optimum transformer frequency ofseveral thousand cycles the transformer would require lower voltages(about 400 volts) to fire a detonator but the power input required wouldbe at least 50 watts. Such power even at the optimum frequency is alsonot likely to be used in communication circuits. The apparatus thereforpossesses a high degree of safety.

The apparatus of my invention provides an electric detonator-firingmeans having a combination of condenser and resistors which alwaysassures a short pulse (less than 1 milli-second) regardless of thedetonator-circuit resistance,

thereby assuring firing of low-thermal-delay detonators within a knowntime interval which can easily be identified by a sharp recordedinstant. Absence of energy except at the firing instant eliminates therecording of noises caused by electrical leaks, poor contacts, crossedwires after the explosion, and other effects.

Experiments have further shown What I claim as my invention is:

1. An electric detonator-flring apparatus comprising a source ofdirect-current energy, a first resistor and a condenser connected inseries across the terminals of said source, a normallyopen switch and asecond resistor connected in series across the terminals of saidcondenser, means for connecting a detonator directly across theterminals of said second resistor, and means for closing said switch.

2. An electric detonator-firing apparatus comprising a direct-currentelectric generator, a condenser connected across the terminals of saidgenerator, a first resistor connected across the terminals of saidcondenser, a normally-open switch and a second resistor connected inseries across the terminals of said condenser, means for connecting adetonator directly across the terminals of said second resistor, andmeans for closing said switch.

3. An electric detonator-firing apparatus comprising a manually-drivendirect-current electric generator, a first resistor and a condenserconnected in series across the terminals of said generator, 2.normally-open switch and a second resistor connected in series acrossthe terminals of said condenser, means for connecting a detonatordirectly across the terminals of second resistor, and means for closingsaid switch when said generator has attained operating speed.

4. An electric detonator-firing apparatus comprising a manually-drivendirect-current electric generator, 9, first resistor and a condenserconnected in series across the terminals of said generator, a secondresistor connected across the terminals of said condenser, anormally-open switch and a third resistor connected in series acrosssaid condenser, means for connecting a detonator directly across theterminals of said third resistor, and means for closing said switch whensaid generator has attained operating speed.

5. An electric detonator-firing apparatus comprising a manually-drivendirect-current electric generator, 9. first resistor and a condenserconnected in series across the, terminals of said generator, a secondresistance of high value connected across said condenser, a normallyopenswitch and a third resistance of low value connected in series acrossthe terminals of said condenser, means for connecting a detonatordirectly across said low resistance, and means for closing said switchwhen said generator has attained operating speed.

6. An electric detonator-firing apparatus comprising a manually-drivendirect-current electric generator, a condenser connected across theterminals of said generator, a high resistance connected across theterminals of said condenser, a normally-open switch and the primarywinding of a transformer and a third resistance of low value connectedin series across the terminals of said condenser, a secondary winding ofhigh resistance on said transformer, means for connecting said secondarywinding to a utilization circuit, means for connecting a detonatoracross said low resistance, and means for closing said switch when saidgenerator has attained oper-v ati'ng speed. I

7. An electric detonator-firing apparatus comprising a manually-drivendirect-current generator, .a first resistor and a condenser connected inseries across the terminals of said generator, a second resistance ofhigh value con- -cluding a switch arranged to be closed after a nectedacross said condenser, a normally-open 15 switch and the primary windingof a transformer and a third resistance of low value connected in seriesacross said condenser, a secondary winding of high resistance on saidtransformer, means for connecting said secondary winding to autilization circuit, means for connecting a detonator across said lowresistance, and means-for closing said switch when said generator hasattained operating speed. I v 8. An electric detonator-firing apparatuscomprising a manually-driven direct-current generator, a first resistorand a condenser connected in series across the terminal of saidgenerator, a transformer having a saturable core and a lowimpedanceprimary winding and a high resistance secondary winding of substantiallymore turns than the primary winding, a normally-open switch and theprimary winding of said transformer and a second resistor connected inseries across said condenser, means for connecting said secondarywinding to a utilization circuit, means for connecting a detonatoracross said second resistor, and means for closing said switch when saidgenerator has attained operating speed.

9. An electric detonator-firing apparatus comprising a manually-drivendirect-current generator, a first resistor and a condenser connected inseries across the terminals of said generator, a high resistanceconnected across said condenser, a transformer having a saturable coreand a low-impedance primary winding and a high resistance secondarywinding of substantially more turns than the primary winding, anormally-open switch and the primary winding of said transformer and alow resistance connected in series across said condenser, means forconnecting said secondary winding to a utiliza-- tion circuit, means forconnecting a detonator across said low resistance, and means for closingsaid switch when said generator has attained operating speed.

10. An electric detonator-firing apparatus for seismograph shot-momenttiming comprising a condenser of high capacitance, a, charging circuitfor said condenser including a direct-current source and a seriesresistor having a resistance of the order of four ohms per volt of thesource voltage to limit the source current to a value less than thecurrent required to fire a detonator, and a series-connected dischargecircuit for said condenser including a switch arranged to be closed whenthe charge on the condenser is substantially at its maximum value, theprimary winding of a pulse transformer whose secondary winding may beconnected to a time-recording circuit, and a pair of detonator terminalsparalleled by a resistor of suificiently low ohmic resistance to assurea maximum time-constant of discharge of said condenser of the order ofone milli-second.

11. An electric detonator-firing apparatus for seismograph shot-momenttiming comprising a condenser of high capacitance, a charging circuitfor said condenser including a manuallycontrolled direct-current sourceand a series resistor having a resistance of the order of four ohms pervolt of the source voltage to limit the source current to a value lessthan the current required to fire a detonator, and a series-connecteddischarge circuit for said condenser insubstantially full charge isbuilt up on said condenser, a low-impedance primary winding of a pulsetransformer having a high-impedance secondary winding connectable to atime-recording 9 circuit and a core including a leg which is readilysaturable by the discharge current, and a resistor in parallel withwhich a detonator may be connected, said last-named resistor being ofsufllciently low ohmic resistance to constitute with said condenser andtransformer primary 9, time-constant of discharge of the order or onemini-second.

GARY MUFF'LY.

REFERENCES CITED UNITED STATES PATENTS Number Number Name Date AsireDec. 13, 1932 Stuart Mar. 9, 1943 Martin Mar. 6, 1945 Weisglass Feb. 26,1946 Paslay Mar. 29, 1949 McKinney Dec. 6, 1949 FOREIGN PATENTS CountryDate Germany Aug. 3, 1933

